Date: Wed, 1 Mar 2006 21:57:07 +0100 From: Rink Springer <rink@il.fontys.nl> To: Julian Elischer <julian@elischer.org> Cc: current@freebsd.org, sos@freebsd.org, "Mikhail T." <mi@aldan.algebra.com>, Brian Candler <B.Candler@pobox.com> Subject: Re: pitiful performance of an SATA150 drive Message-ID: <20060301205707.GA65200@il.fontys.nl> In-Reply-To: <4405EFE9.6030807@elischer.org> References: <200603010505.k2155HfQ003205@aldan.algebra.com> <20060301144124.GA14411@uk.tiscali.com> <4405EFE9.6030807@elischer.org>
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> I believe that linux uses bufferring in their 'raw' disks so that you > may be actually doing larger > reads and writes than you know.. (of course my knowledge of Linux is a > bit old so > they may have changed that) Linux 2.5+ will always queue I/O requests in PAGE_SIZE chunks (4KB on i386) or less. These tiny requests will be concatinated by the disk elevator if possible; for example, reading 64KB from block 0 once would result in requesting 16 times 4KB, which will be translated to a single "Read 64KB from block 0" request. Therefore, the PAGE_SIZE cache (also known as the buffer cache, which was merged with the page cache in the 2.5 tree) does not hurt performance one bit. I have no clue what FreeBSD does on this end. -- Rink P.W. Springer - http://rink.nu "Richter: Tribute? You steal men's souls, and make them your slaves! Dracula: Perhaps the same could be said of all religions." - Castlevania: Symphony of the Night
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